Tub Draining Slowly

i just finished the new tub and shower, used it for the first time and it doesnt seem to drain quick enough it holds a small puddle while showering and i can hear it gulping, it is a new drain, trap is clean. im stumped

ALL fixtures must be vented. That's the what is causing the gulping. This makes me wonder if there is a trap and if the drain is large enough. A shower needs a 2" drain. Tubs benefit from a large drain also, but 1-1/2" will work.